Half-sandwich Complexes of Ruthenium Supported by N-Heterocyclic Carbene Ligands PDF Download
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Author: Van Hung Mai
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Languages : en
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This thesis presents the preparation and catalytic reactivity of novel half-sandwich ruthenium complexes supported by N-Heterocyclic Carbene (NHC) ligands. The cationic half-sandwich ruthenium complexes [Cp(IPr)Ru(CH3CN)2]+ show interesting reactivities toward the transfer hydrogenation of different unsaturated substrates, such as ketones, olefins, N-heterocycles, and nitriles. Kinetic studies disclose that a neutral trishydride ruthenium complex is actually involved in the catalytic cycle, playing the role as a resting state. Further investigations on the sub-class of trishydride ruthenium complexes bearing NHC ligands (Cp'(NHC)RuH3) reveal that these complexes have an unusual and great catalytic performance toward the hydrodefluorination (HDF) of fluorinated aromatic and aliphatic compounds. The combined kinetic studies, cross-over experiments and rate law analysis suggest an unusual mechanistic pathway for the Cp*(IPr)RuH3 catalyzed HDF. This study is one of the rare examples where isopropanol is employed as a reducing agent for the metal-mediated HDF reaction. A class of silyl dihydride ruthenium complexes, derived from Cp(IPr)RuH3 are prepared. These silyl hydrido derivatives are great compounds for the study of the inter ligand hypervalent interaction (IHI), an interesting phenomenon for many non-classical silane complexes. This study also suggests that the replacement of phosphines by their isolobally analogous NHC ligands result in stronger IHI interactions in the corresponding compounds. Another type of non-classical interaction was systematically scrutinized in a ii series of new cationic and neutral silane sigma complexes of ruthenium bearing different silyl moieties. These new NHC-supported ruthenium complexes allow for direct comparation with the known phosphine analogues, which reveals interplay of steric and electronic factors on the extent of Si-H complexation to metal and the extent of additional interligand interactions between Ru-Cl and chlorosilane ligand. Finally, new trishydride ruthenium complexes bearing NHC ligands (Cp'(NHC)RuH3) catalyze the H/D exchange reaction of various N-heterocycle substrates; their catalytic performance can be considered as one of the mildest, and most efficient approaches.
Author: Van Hung Mai
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Languages : en
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This thesis presents the preparation and catalytic reactivity of novel half-sandwich ruthenium complexes supported by N-Heterocyclic Carbene (NHC) ligands. The cationic half-sandwich ruthenium complexes [Cp(IPr)Ru(CH3CN)2]+ show interesting reactivities toward the transfer hydrogenation of different unsaturated substrates, such as ketones, olefins, N-heterocycles, and nitriles. Kinetic studies disclose that a neutral trishydride ruthenium complex is actually involved in the catalytic cycle, playing the role as a resting state. Further investigations on the sub-class of trishydride ruthenium complexes bearing NHC ligands (Cp'(NHC)RuH3) reveal that these complexes have an unusual and great catalytic performance toward the hydrodefluorination (HDF) of fluorinated aromatic and aliphatic compounds. The combined kinetic studies, cross-over experiments and rate law analysis suggest an unusual mechanistic pathway for the Cp*(IPr)RuH3 catalyzed HDF. This study is one of the rare examples where isopropanol is employed as a reducing agent for the metal-mediated HDF reaction. A class of silyl dihydride ruthenium complexes, derived from Cp(IPr)RuH3 are prepared. These silyl hydrido derivatives are great compounds for the study of the inter ligand hypervalent interaction (IHI), an interesting phenomenon for many non-classical silane complexes. This study also suggests that the replacement of phosphines by their isolobally analogous NHC ligands result in stronger IHI interactions in the corresponding compounds. Another type of non-classical interaction was systematically scrutinized in a ii series of new cationic and neutral silane sigma complexes of ruthenium bearing different silyl moieties. These new NHC-supported ruthenium complexes allow for direct comparation with the known phosphine analogues, which reveals interplay of steric and electronic factors on the extent of Si-H complexation to metal and the extent of additional interligand interactions between Ru-Cl and chlorosilane ligand. Finally, new trishydride ruthenium complexes bearing NHC ligands (Cp'(NHC)RuH3) catalyze the H/D exchange reaction of various N-heterocycle substrates; their catalytic performance can be considered as one of the mildest, and most efficient approaches.
Author: Mathieu Baffert
Publisher:
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Category :
Languages : en
Pages : 0
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The goal of this PhD was to elaborate supported Ru-NHC catalytic materials based on hybrid organic-inorganic materials having imidazolium units perfectly distributed within a silica matrix. Passivation of these imidazolium materials followed by formation of NHC-carbene and reaction with [RuCl2(p-cymene)]2 provided these well-defined surface sites of general structures RuCl2(NHC)(L), where L was para-cymene (p-cymene) or THF depending on the reaction conditions, which could be further replaced by PMe3. These systems were then tested in the hydrogenation of CO2 in presence of amine to give formamides. The mono-NHC systems were highly active only in the presence of PMe3 ligands, but suffered from Ru leaching, evidencing the low stability of the NHC-Ru bond under the reaction conditions. On the other hand, dinuclear bis-NHC Ru systems were also developed, and they displayed much improved activity and stability in the hydrogenation of CO2 in the presence of PMe3 compared to the mono-NHC systems. This allowed the use of much higher reaction temperatures (200 °C) and provided heterogeneous catalysts with performances close to those obtained with the best homogeneous catalysts, Cl2Ru(dppe)2.
Author: Ka-Ho Chan
Publisher: Open Dissertation Press
ISBN: 9781361379714
Category :
Languages : en
Pages :
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This dissertation, "Ruthenium-N-heterocyclic Carbene and Ruthenium Acetylide Complexes Supported by Macrocyclic Porphyrin or Tetradentate Schiff Base Ligands: Synthesis, Structure and Catalytic Applications" by Ka-ho, Chan, 陳嘉豪, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled RUTHENIUM-N-HETEROCYCLIC CARBENE AND RUTHENIUM ACETYLIDE COMPLEXES SUPPORTED BY MACROCYCLIC PORPHYRIN OR TETRADENTATE SCHIFF BASE LIGANDS: SYNTHESIS, STRUCTURE AND CATALYTIC APPLICATIONS Submitted by Chan Ka Ho for the degree of Doctor of Philosophy at The University of Hong Kong in March 2015 Transition metal-catalyzed C-C and C-N bond formation reactions are important transformations in synthetic organic chemistry. In the endeavor of this thesis to develop robust/versatile catalysts for these reactions, the trans effect imposed by N-heterocyclic carbene (NHC) and acetylide ligand onto ruthenium complexes supported by macrocyclic porphyrin or tetradentate Schiff-base ligands was studied. The catalytic activity of these novel ruthenium complexes towards carbene and/or nitrene transfer and insertion reactions was also explored. II A series of bis(NHC)ruthenium(II) porphyrin complexes [Ru (Por)(NHC) ] were synthesized by deprotonation of imidazolium salt using a strong base. These complexes displayed unprecedentedly high catalytic activity towards carbene/nitrene transfer and insertion reactions, including alkene cyclopropanation and aziridination, carbene C-H, S-H, N-H and O-H insertions, and nitrene C-H insertion with product -1 turnover frequency up to 1950 min . Carbene modification of N-terminus of peptide o II at 37 C was achieved. Chiral [Ru (D -Por)(NHC) ] catalyst led to highly 4 2 enantioselective carbene/nitrene transfer and insertion reactions with up to 98% ee. DFT calculations revealed that the strong σ-donor strength of trans axial NHC ligand stabilizes the formation of metal-carbene and metal-nitrene intermediate from decomposition of diazo compounds and organic azides, which is crucial for the transition metal-catalyzed oxidative C-C and C-N bond formation reactions to proceed under mild reaction conditions. II A series of ruthenium Schiff-base complexes cis-β-[Ru (Schiff-base)(CO) ] were synthesized and characterized. These complexes showed high catalytic activity towards enantioselective cyclopropanation, carbene C-H and Si-H bond insertions. II t The cis-[Ru (2-CPh -4- Bu-Schiff-base)(CO) ]-catalyzed intermolecular 3 2 cyclopropanation of styrene with EDA in CH Cl afforded desired cyclopropane 2 2 product in 90% isolated yield and 95% ee with a product turnover number of 9000. Excellent trans- and high enantioselectivity were observed with wide substrate scope, including conjugated, electron-rich, electron-deficient and aliphatic terminal alkenes. Carbene C-H and Si-H insertion reactions proceeded smoothly with II t cis-[Ru (2-CPh -4- Bu-Schiff-base)(CO) ] as catalyst, giving the desired products in 3 2 82-97% yields with excellent enantioselectivity (up to 99% ee). The same complex was also catalytically active towards intramolecular cyclopropanation and intramolecular alkyl carbene sp C-H bond insertion to give cis-products with up to 99:1 cis: trans ratio and with excellent enantioselectivities (up to 98% ee). DFT calculations on the intermolecular cyclopropanation catalyzed by II cis-β-[Ru (Schiff-base)(CO) ] revealed that among the ruthenium-carbene intermediates possibly involved in the reactions, the cis-β species are more stable than their trans isomer with
Author:
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Category : Organoruthenium compounds
Languages : en
Pages : 468
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Author: Allen J. Bard
Publisher: CRC Press
ISBN: 1135535795
Category : Science
Languages : en
Pages : 707
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The first source on this expanding analytical science, this reference explores advances in the instrumentation, design, and application of techniques with electrogenerated chemiluminescence (ECL), examining the use and impact of ECL-based assays in clinical diagnostics, life science research, environmental testing, food and water evaluation, and th
Author: Kar-Yee Lam
Publisher:
ISBN: 9781361034415
Category : Iron compounds
Languages : en
Pages : 290
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Author: Kai Yang Wan
Publisher:
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Category :
Languages : en
Pages : 0
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In this thesis, the synthetic protocol for a new class of enantiopure, primary-amine tethered N-heterocyclic carbene (NHC) ligands is described. The synthesis, coordination chemistry, and applications in catalysis for three ligands from this class with general formula (S,S)/(R,R)-H2N-CHPh-CHPh-NHC (NHC = -NCHCHN(C)R, R = Me, tBu, or Mes) are reported. The imidazolium salt of these ligands can be prepared in high yield and purity from the SN1 reaction between chiral sulfamidates and the corresponding N-substituted imidazoles. The method of coordination of the NHC ligands to metals depends on the acidity of the C-H functional in the imidazolium salts. Silver and copper compounds can be prepared in high yield with the ligand to the metal ratio of 2:1 or 1:1. Ruthenium, iridium, and rhodium complexes can also be prepared via transmetallation from the silver or copper reagents, intramolecular base deprotonation, or C-H oxidative addition. Four ruthenium complexes and two iridium complexes based on these ligands were proven active for ketone hydrogenation, under relatively mild condition (50°C, 25 bar H2(g)). Three half-sandwich ruthenium compounds containing Cp (cyclopentadienyl) or Cp* (1,2,3,4,5-pentamethylcyclopentadienyl) are highly active aryl and alkyl hydrogenation catalysts with TOF (turnover frequency) up to 67 s-1, TON (turnover number) up to 104, and ee (enantiomeric excess) up to 86%. An experimental and computational study of the half-sandwich ruthenium systems suggests that the heterolytic splitting of dihydrogen over the metal-amido bond and hydride transfer from the catalyst to the substrate can both be rate-determining. An alcohol-assisted mechanism was also calculated to explain the rate enhancement when the catalysis was conducted in polar, protic solvents such as 2-PrOH. A full experimental and computational study was also performed for a Fe(P-NH-P') system. Similarly, heterolytic splitting and hydride transfer are the two most energy demanding transition states. In addition, the enantiodetermining step (EDS) of this asymmetric ketone hydrogenation catalyst was calculated, and the origins of enantioselectivity were summarized as steric repulsion, the high compressibility of the backbone, and H-bond contributed stabilization.
Author: Silvia Diez-Gonzalez
Publisher: Royal Society of Chemistry
ISBN: 1782626816
Category : Science
Languages : en
Pages : 637
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Book Description
In less than 20 years N-heterocyclic carbenes (NHCs) have become well-established ancillary ligands for the preparation of transition metal-based catalysts. This is mainly due to the fact that NHCs tend to bind strongly to metal centres, avoiding the need of excess ligand in catalytic reactions. Also, NHC‒metal complexes are often insensitive to air and moisture, and have proven remarkably resistant to oxidation. This book showcases the wide variety of applications of NHCs in different chemistry fields beyond being simple phosphine mimics. This second edition has been updated throughout, and now includes a new chapter on NHC‒main group element complexes. It covers the synthesis of NHC ligands and their corresponding metal complexes, as well as their bonding and stereoelectronic properties and applications in catalysis. This is complemented by related topics such as organocatalysis and biologically active complexes. Written for organic and inorganic chemists, this book is ideal for postgraduates, researchers and industrialists.
Author: Sun Hwa Lee
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: J. Silver
Publisher: Springer Science & Business Media
ISBN: 9401121400
Category : Science
Languages : en
Pages : 316
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This book is designed to be of use to the reader in two different ways. First, it is intended to provide a general introduction to all aspects of iron chemistry for readers from a variety of different scientific backgrounds. It has been written at a level suitable for use by graduates and advanced undergraduates in chemistry and biochemistry, and graduates in physics, geology, materials science, metallurgy and biology. It is not designed to be a dictionary of iron compounds but rather to provide each user with the necessary tools and background to pursue their ,individual interests in the wide areas that are influenced by the chemistry of iron. To achieve this goal each chapter has been written by a contemporary expert active in the subject so that the reader will benefit from their individual insight. Although it is generally assumed that the reader will have an understanding of bonding theories and general chemistry, the book is well referenced so that any deficiencies in the reader's background can be addressed. The book was also designed as a general reference book for initial pointers into a scientific literature that is growing steadily as the understanding and uses of this astonishingly versatile element continue to develop. To meet this aim the book attempts some coverage of all aspects of the chemistry of iron, not only outlining what understanding has been achieved to date but also identifying targets to be aimed at in the future.
